Spark plug



May 22,1934. G. MIPAULSON v 1,959,639

- I SPARK PLUG Filed May 27, 1932 Patented May 22, 1934 SPARK PLUG George M. Paulson, New York, N. Y., assignor to The B. G. Corporation, New York, N. Y., a corporation of New York Application May 27, 1932, Serial No. 613,807

2 Claims.

This invention relates to spark-plugs, and more especially to spark-plugs for use in aviation engmes.

The object of the invention has been to provide 5 a spark-plug which would give superior, reliable and long service under the conditions to which aviation spark-plugs are subjected, and even when very high compressions, with extreme supencharging, are resorted to.

A further object has been to provide an aviation spark-plug which, under most diflicult conditions, would not heat up to the point of causing pre-ignition.

A further object has been to provide a construction which would protect the core and keep it relatively cool under such conditions.

A further object has been to use a groupment of sparking points giving as long an electrode life as possible, and also allowing of adjustment, and

still to find a way to cool these points and take the heat away so that they should not cause preignition or burn away rapidly.

The spark-plug of the invention is of a type especially suitable for aviation purposes, in which the chamber of the shell, into which the core projects, is partly closed or is protected by an apertured disc or cup known as a baflie, and in which this bafile serves as the grounded electrode. Baffles of different kinds have been known for many years, and have been used for various purposes in aviation spark-plugs, and also in automobile spark-plugs. To some extent they may shield the core chamber and the core from lubricating oil, and, by virtue of their apertures, they may cause the gases to flow in and out with a cleaning action. In aviation spark-plugs, a baflie electrode should be capable of sufficiently protecting the core from intense radiant heat, which may be as high as 2600 F., and it must be able to function and not superheat itself or the plug to a point of failure.

Baflies have been used which are composed of a metal or alloy different from that of the shell and which is resistant to the spark in the presence of cylinder gases. Prior to this invention, the practice was to insert the bafile tightly into a seat in the lower end of the shell and to lock it and powerfully grip it by forcing the shell over the margin of the baflie, clamping it against a shoulder at the base of the seat.

Aviation spark-plugs having a construction of this kind were subject to failure after longer or shorter periods of'use or test in engines operated at moderately high compressions, and were unequal to service under the very high compressions and the corresponding temperatures and combustion conditions that spark-plugs of the present invention can withstand without becoming so hot as to cause pre-ignition, or suffering much burning away of the sparking points of the bafiie.

The surprising results which have been obtained with plugs embodying the present invention have been due largely to a different manner of joining the baflie to the shell. I have found not only that the mechanical locking-in of the bafiie. might be dispensed with, and that the electrode baffle could be securely held in an open seat by a fused bond, but also that spark-plugs made in this way would not cause pre-ignition, either at the beginning or after extended use, or in course of test under most severe conditions. I have found, also, that the sparking points of such baflies burn away but slowly. The invention is concerned, more especially, with a spark-plug construction which 'aflords' a multiplicity of substantial sparking points, three or four for example, to secure the long electrode life already mentioned, and which makes this long electrode life good by rapidly taking away the heat, and which at the same time 3 sufliciently guards the core, and which also enables the points to be adjusted.

Other features of the invention will become apparent as the specification proceeds.

In the accompanying drawing forming part 35 hereof:

Fig. l is a view of one of the spark-plugs of the invention, partly in elevation and partly in longitudinal section;

Fig. 2 is a view looking at the er end;

Fig. 3 is a longitudinal section on an enlarged scale of the inner end portion of the plug; and

Fig. 4 is a detail section illustrating a form of the invention which has been utilized with advantage to satisfy extreme requirements.

The spark-plug shown in this drawing, as illustrating the invention, has a shell 2, screw-threaded on the outside for insertion into the engine casting. This shell is made of any suitable free-tuming steel. The shell surrounds a chamber 3 of known purpose, into which extends the core consisting of the central spindle 4, with its terminal electrode 5, and insulation 6, preferably of mica.

In the lower end of the shell there is a counter-bore providing a shoulder '7 and a circumm5 ferential wall 8, the surrounding wall being inclined as shown. Into this seat a thick cupped disc 9 is laid, and a circle of brass wire placed over the crevice is melted in the presence of flux to form the fused bond 10. This bond unites the no side and inside fillets ofthe bond increase the rate of heat conduction from the bafile and its points to 81 the shell.

The disc is composed of a suitable metal or alloy, for example, a nickel-manganese alloy,

which will lastingly resist the spark, and which.

will permit the sparking points 11 to be bent repeatedly to keep the proper gap until the end of the life of the plug. The disc is cupped so as to protrude into the combustion space of the cylinder, and it is cut to provide apertures and a group of sparking points surrounding the center electrode. However, advantage may be sacrificed and an annular spark gap may be used.

This electrode baflle must be heavy in order to stand up and to save itself and the core from excessive heating, but not so heavy as to be an accumulator of heat. The heat taken by the baiile and its points is rapidlydissipated into the shell through the heat-conducting metal of the bond, with the result that the spark-plug as a whole is kept cooler than would-otherwise be possible in a. construction having so much metal at the gap.

Notwithstanding very high compressions and temperatures, the rate at which heat is carried away from the baflie prevents pre-ignition. For the same reason the life of the sparking points is much prolonged, and adjustment of the spark gap by bending the prongs need be relatively infrequent.

It is an advantage, and may be of vital importance, that the aviator or his mechanic can adjust the gap without returning'the plugs to the manufacturer. A few easy adjustments are sufiicient in these plugs during exceptionally long use.

For best results, the outer or annular portion 12 of the baffle, which is in contact with the bond,

is made thicker than the stout sparking prongs. This is carried onward in Fig. 4, in which the rim of the baflle is made with a vertical extension 15 to provide a deeper fused joint with the shell. Experience has demonstrated that such plugs will work in engines operated beyond the resistance of plugs such as shown in Figs. 1 and 3.

In combination with the fused joint between the circumference of the multiple-pronged baflle and the shell, the provision of relatively large spaces between the prongs has proved beneficial. In former aviation plugs having locked-in electrode bailies, the openings between the prongs were narrow and slotted. The plugs of my construction stay cooler when comparatively broad orifices 13 are made in the baille, these orifices being constricted, however, at the points where they communicate with the space 14 around the center electrode. A wide triangular form for the orifices, with the bases of the triangular openings away from the center, is excellent, though other forms may be used.

Spark-plugs made in accordance with the invention have a useful life two to three times that of the plugs having locked-in baflies. They have given service up to '750hours, and the average life is about 500 hours as against 200-250 hours for the former construction. They perform successfully, without causing pre-ignition, in dynamometer endurance tests of 100 hours, or more, in aircooled engines operated at full throttle, with the compression raised and the cylinders supercharged to a point at which, the other plugs fail .in the course of a few hours, if not immediately.

40%, by super-charging or super-compressing,

without danger of pre-ignition from the plugs and with a longer electrode life than the former plugs had in normally operated engines.

An explanation for these remarkable gains is, I believe, that although in the older construction the baille was apparently rigidly and integrally incorporated with the shell, nevertheless the gases did manage to enter the joint, causing deterioration, whereas in my improved plugs there is always a safe drawing-oil of heat from the electrode baflie to the shell, in consequence of which the bailie does not-attain a pre-ignition temperature and the sparking points 'do not quickly burn away, though they be exposed to the most intense temperatures and exceedingly high compressions.

In addition to this, and in cooperation, other features of the invention are important. There is a balance to be observed between the shading of the core by the baflle and the amount and distribution of metal in the grounded'electrode, which can not be stated precisely; but for any particular set of conditions the proper relation can be arrived at by following this specification.

A bond of metal different from those of both the baflle and the shell, of good heat conductivity, and of relatively low fusing point, such as brass, silver solder, or the like, has been entirely adequate to exceptional demands, and it is a very cheap way of uniting the parts. As far as experience shows nothing more is required, but obviously a mechanical lock could also be provided.

I claim:

1. In a spark-plug, the combination of a shell of one metal, an internally-pronged electrode battle of metal resistant to the spark and bendable foradjustment of the prongs, and a fused the circuit of the baflle electrode with the shell.

GEORGE M. PAULSON. 

